System of radio communication



June 6, 1944.

E. H. ULLRICH SYSTEM OF RADIO COMMUNICATION Filed Nov. 8, 1941 PatentedJune 6, 1944 SYSTEM OF RADIO COMMUNICA'IION Edward Hill Ullrich, London,England, assignor to International Standard Electric Corporation,

New York, N. Y.

Application November 8, 1941, Serial No. 418,280 In France May 21,1940

(Cl. Z50-6) 8 Claims.

, This Yinvention relates to a Vsystem of radio n communication and moreparticularly to radiocally compensated at the reception.

A preferred embodiment of the invention which will now be explained withreference to the single gure of the attached drawing consists in thesimultaneous transmission of two or more different wave lengths and inthe adjustment of the receiver so as` to receive waves and combine themin a manner to isolate the group of direct signals from the group offirst echoes.

The apparent height of the ionosphere which reflects the electromagneticwaves depends on the wave length. Notwithstanding this, changes in thisapparent height with changes in the wave length will be very slow exceptfor the so-called critical frequencies. Within the scale of the shortwaves with which we are particularly concerned, the echoes of two waves,M and A2, spaced in frequency by a few tens of kilocycles per second maybe considered as coming from the same layer of the ionosphere. Bysimultaneously sending on the two wave lengths M and k2, the direct waveM will follow the same path as k2, and the rst echo of wave length Mwill follow the same path as the rst echo of wave length lf2, etc. Theresult of this is that the two direct waves as well as the pair ofechoes will arrive together, but the echoes will lag behind more andmore. At a given moment, there will be in a receiver tuned to receive atwave length M, a direct wave and a series of echoes. rlhe same thing istrue for a receiver tuned to receive the wave length x2. In' order tosimplify the explanation, a single echo will be considered.

In the receiver, the direct waves will have the same relative phase asthey had at the instant of emission in the transmitting antenna. Bymodifying the wave length and the phase of the wave A2 by a frequencychanger (or a, heterodyne circuit) in a manner to bring its frequency tothe same frequency and to the same phase as wave M and by super-posingthese two waves, the two will be added arithmetically. l

Like the frequency of the wave and the speed of its phase variation, theheterodyne oscillator will change in phase during the time required forthe wavesto travel from the transmitterto the receiver. If the phase ofthis oscillator is so arranged that the direct waves which are receivedwill be aiding in phase, then the echoes which take longer to traversethis space will be added vectorially at an angle which depends on thediierence of frequency corresponding to wave lengths M and )l2 and theduration of the interval between the reception of the direct wave andthe rst echo. The frequencies of two waves are so selected that the twoechoes will be substantially cancelling one another when the directwaves are added to one another. On the other hand, the system can be soarranged that the direct waves will be cancelling one another and theechoes will be added to one another. It is possible, therefore, toisolate the pair of direct waves and the pair of echoes and to utilisethese two pairs, e. g. by combining them in such a manner as to increaseas much as possible the relationship between the signal and theparasites. Let

p(t) be the low frequency wave to be transmitted sin wt the carrier wavecorresponding to the wave length M sin (w+6)t the carrier wavecorresponding to the wave length A2.

If at the receiver the direct wave M is Amt) sin wt where A is aconstant, the echo will have the form Y Beit-T) sin w(t-T) Where B is aconstant and T the interval of time between the instants when the directwave and the rst echo are received.

The wave at the input of the receiver tuned to wave length M will havethe form R1=A p t sin wt+B p(t-T) sin Kt-T) (1) and the wave at theinput of the receiver tuned to A2 BgoG-T) sin (w-i-H) (t-T) (2) If theheterodyne is arranged to reduce all the frequencies of the wave form R2from 0/21r, we will get To indicate Athe values, a lag T of microsecondswill notmaterially Vdiminish the quality of a commercial telephoneconversation. "On the other ha'nd, a lag of 1A millisecond may be very ldamaging. In this case, since RliRl isr3 `decibels .higher than 'theratio of the wave-or the echo to the Jparasites in R1 `or.Rarespectively. If all 'the power were concentrated inthechannel ofwave.length XI, then the 'lastmentioned relationship would also be augmenteddirect` nected in pairs to two receivers 8 and I0 of any suitablewell-known type. Their outputs are connected over individualtransformers I 4 and MI5 in opposition to a telephone receiver orsimibyf:3..decibels. Therefore, the. use of two waveV lengths will notcausefany reduction in the-ratio between the signal and the parasites inthe direct wave or in the echo. Quite on the contrary, ac cording toanother feature of the present inven-v tion, this ratio can be increasedby suitably mix--y ing -the `signals Ri-IeRz1 and R`1..-Rz1gbefore-forafter detection, but after having retarded the In practice, the mixingis accomplishedv afterA detection because the height of theY reflectinglayer is notrigorously constant-*and becausethe relative phase of theadditive and subtract/ive signals varies. It is, however, possibleautomatically to control thefphase of th htei'odyn'e QSCillater in anySuitable i' lWell-knvvr'i. manner S0 that the Waves of the signals orEquationsand 6 Vremain in phase. 4 ,A a

It should be noted that the condition e'irpressed by the relationship 4is not a necessary condition for isolating the pair of direct waves fromthe pair of echoes. As armatter of fact, 1in accordance withtherelationships 1 and L3, one getsV isolated. By suitably modifying thephase of the heterodyne, the ipair of direct waves can be isolated in asimilar manner. v The conditionfl gives, therefore, onlythe optimumrelationship between the signal andthe parasites.

The -only gure of theattached drawing schematically illustrates anembodiment of the 4inventionp n a In this figure a pair of transmitters"I6 and I'I respectively tuned to the wave lengths M and A2 are coupledto 1an antenna and simultaneously keyed by a keying means I8. a tunedantenna circuit I is connected between the two filters 2 and 3 which arerespectively tuned-to to the wave lengths M Vand X2. The output of thefilter 2 is connected directlyito the primary winding of a transformerI2 having two secondary windings-andthe output of the filter 3 isconnected to afrequency changer f4 which is connectedvto aheterodyneoscillator 6 through aphase adjuster 5. The output of the the change offrequency, in other words, tothe wave length of the .other channel. Theoutput ofY In theV receiver,

. cies of-thetwo transmitter waves.

Ylar translating device. 9 is a retardation circuit forretarding-the'waves in one receiving branch :by TV as ,previouslyexplained.

The operation of such circuitv will be clear from the above, thetransformers I2 and I3 permitting the application of the outputs of twochannels inY series in one and in opposition in the other. In order toreduce to a minimum the effect ofthe frequencies Vin a system embodyingAY such receiver, the frequency of A2 may beobtained in the transmitterbeginnin'gwith XI and then adding or subtracting'the difference between`these two frequencies. In the same manner, the' heterodyneoscillator inthe receiver may have 'a theoretical frequency equal to the differenceVof frequencies corresponding to M and A2. lIn 'this manner, thefrequency of the heterodyne will-be low and it willV bev easy to obtainfrequency stabili-'Zation'which is of 'great importance to the properfunctioning of the system. Y

iInorder to simplify the explanation of theV operation, we have assumedin vthe above that only lthe 'frequency `of onewave will be changed Vinorder to convert Litinto the second frequency.

In practice,` the frequencies of two waves will be changed byv reducingthem to theV same mean frequency. InV this oase, the frequency of a beatoscillatormay be obtained from the frequency of the other beatoscillator by the addition or sub-'- traction of` the difference betweenthe frequen- -A communication Vsystem embodying the feaitures of thepresent invention .is obviously not limited to the use of twosimultaneously transmitted waves. If Vfor example, three waves aretransmitted, then by Vcombining in a suitable manner the signals of thethree receivers, two of the. waves may be 'suppressed andonly thedesired w'ave preserved. We 'will have:

aififiewsin artigiani-Tann o1 j (tl-T1) +C p(t-T2)sin cliff-T2) R2=Ap()SiI1 w2t|B` p(-T1)Sin l Y Y .out-,T0 +Co(t--Tt)sinjw2r(t-T2) Byheterodyning in order to` obtain: Ri=Ac siniat+f-1 r1f sin[wig-T1)+1+T1(w-w2)]+Q(;Tz) sin Y Y Y r'ldi-(wTz)+1,+Tz(wxw2)] R=41 0sin (wif-i-fQ-l-BM-tl-Tr) sin [wi T1) -l- 2IT1(w1rg:2)] -I- Co (t- T2)sin v v [w1(-T2`)VY|f2+7:2(011-012)] and by adding the three waves R1,Rc1., :and Rai, we will obtain three vectorial diagrams for. the threedirectwaves and1for-each` grounfof Vwaves corresponding-to the first orto fthe second'echo,

, frequency changer is connected withaffilteri l Vtuned to the new Wavelength obtained after @.ijafcaeae egli-2a..; j L j no;

f where. thersame :sign-will be obtained rinunciations 1'? and: 8 andthe same sign in -Eqiations T9 and -,but not necessarily lthe samesignin the twopairs 'of equations. Bycon'sideringfthe case when all thesigns are positive:

(T2-TD (w1 w2)=2(M-.-N),1`|v ('11)v (T2-,T0 (1+ug3)=2(mn)1 (12)relationships where M, N, `m, n 'are whole numbers. The conditions 11and 12 determine Q2 and w3 andthe conditions 7 and 8 determinen and 'e2V'for the given values of M,`N,m, nlf The sum ofthe waves R1, R21 and R31is 4therefore independent of the echoes, and the directy wave willVsubsist therein at least unless e1 and e becomegequalto l 3respectivelmN' and' n' being whole numbers. This last case can be easilyavoided by choosing in `a suitable manner the values of M, N, m, V11except inthe case where`Ti=3p (T2-T1),` p being a whole number, havingthus isolated the directl wave, it can be` separated from R1 and R2 andrie-,establish the above case where we "owavesl vInstea` fdep'hasing R21and R31 from ei' and er, respectively,gthe system may also be providedin such a'manner that these dephasing angles beequal `to zeroand'thatv`R1, R21, and R31 be amplified to"different`degr`ees a, b, cbefore adding them'. The following are the conditions for the closing ofthe vectorial diagram of the first echo:` I, j Y w-l-b-wSTi (w1-waiversT1 (w1-w3) =0 f b sin T1v (w1-w2)'+c sin Ti (w1-w3) =0 and, `for thesecond echo,

a+b,wsTa--(u 11wz) +cus(w1-w3) =0 Al) Sin `T2 (wn-wz) |c sin T2 (w1-w3)=0 'Iliese'four 'equations determine the four quantities `b/a, c/ae1-n2, and wi--ws as a function of TiandTaV 'Y GenerallyL speaking, ifthe system 4utilises n waves, there will be v2(1L-1) conditions whichmust be although these Aconditions can always be satis- It is to be`noted that the Wave lengthsare so close to one another that if desiredthey can be transmitted'by the same output stage Vof the transmitter,-The installation cost of the transmitter is,-therefore, very small.

The adjustmenty of the transmitter and the receiver may be yeffected inaccordance with one of the features of the present invention bytransmitting an impulse preferably at a. predeterminedfrequency ofrepetition, e. g. 100 or 200 times per second. iThis impulse or seriesof impulses is receved and detected at the receiver and then applied to'an` indicating apparatus, such as a cathode ray` oscillator, the spot ofwhich'is subjected toa well-known sweep system, e. g, horizontally tosweep the frame of the oscillograph at a predetermined speed. In thecase where a series of impulses is used, the sweeping in the receiverwill be synchronised in a Well-known manner. Thus the direct impulse andits echoes will appear on the oscillograph frame and the leg can bemeasured to determine the optimum frequency of the second wave withrespect to the first wave in accordance with relationship l in the caseof two waves, n being suitably chosen. In the case of a plurality ofwaves, it will usually be always possible to nd frequencies which`permit the addition of all di- `satisfied and 2(n-1) unknowns,L

rect-Waves or all the echoes of the nth scale with a sufficiently smalldisplacement.

'- The lag A.ofthe different waves will generally be constant duringlong intervals of time. It will, therefore, .be suiiicient for thepractical application of the above described system if the regulationwere effected at relatively widely spaced times, e. g. -once every4hour. The different waves are not subject to selective fading, but theweakening of an entire wave-carrier and side bands-.is common enough. Inpractice, the use of more. than onefwave with suitable lag eliminates.the effect.. of fading on the connection. The cost of the .firstinstallation may be reduced by giving up the simultaneous use of thedifferent Waves.V In: this case, in accordance with another featureofthe invention, the fading will be reduced by selecting the strongestwave, e. g. by means of a'mechanical or electrical relay.

' A system embodying features of the present invention will, therefore,have two principal advantages: Improvement of the quality andsuppression: of` fading. Although two or more wave lengths: must beemployed, those wave lengths can: be employed which in .practice wouldother- Wise be useless on account of the phenomenon of echoes.\ l

.- The invention is applicable to the elimination of Aechoes originatingin atmospheric layers. However, theA invention is applicable also tocases wherethe echoes are produced by the presence of obstacles in thepath of the waves, e. g. mountains or even movable objects. providedthat the lag of the echo does notvary too rapidly.

It will be obvious that the inventionis not limited vtothe embodimentsherein disclosed, but that itis capable ,of numerous modifications andadaptations without departing-from the spirit thereof. v

.What is claimed is:

1. A radio signalling system comprising a transmitter having means forgenerating a plurality of carrier waves of different frequencies, meansvfor modulating said carrier waves with theV same signals, and means forradiating said modulated carrier waves, and a receiving arrangementcomprising means for abstracting energy from said modulated carrierwaves means for, convertingv the received waves t0 the same frequency,a,` phase adjuster for converting the directly received waves at thedifferent frequencies to the same phase, two receiving branches, meansfor isolating direct waves in one of said branches and echo wavesproduced by reflections in the other of said receiving branches, anoutput circuit foreach of said branches coupled to a` circuit includingan indicating device and a retardation circuit in one ofsaid outputcircuits whereby the direct signal `waves and the echo signal waves areadditive in the circuit of said indicating device.

A 2. A radio signalling system according to claim 1 wherein saidretardation circuit retards the direct signal waves an interval equal tothe interval between the arrival of the direct signal and the rst echo.

3. In a radio signalling system a transmitter comprising means forgenerating a plurality of carrier waves of different frequencies, meansfor modulating said carrier waves with the same signals, and means forradiating said modulated carrier waves, and a receiving arrangementcomprising means for abstracting energy from said radiated carrierwaves, means for segregating said different frequency waves in separatecircuits, means for converting ,they received 'wavescf the different.frequencies to -thegsame frequency,`

means' for'modifying the .relativeyphasesl of thel received `Waves -ofldiierent frequenciesgns-uch manner thatv` 'the directly'. receivedwaves fareriin theV same phase, 2' al circuit vcomp'rising.; two

assurde c eivmia"breiiths and en"cutputcircuitincludmgbranchesfandne'ans for impressing ,saidfc'on-r` v verted ldirect'wavesAand echoesproduced by re-f flections' in vsuclfiinanner upon'lsaid.'last-'men` tionedicircuitsthat in one branch said;- direct wavesare additive in effect vand :said .echoes `subv sta-ntially neutralizeeachother and in the;.oth'er branch v said vdirect waves' f.substantially neutralize :each other and' said echoes are additive`inreilect' and an loutputcircuit including an indicating dee vicecoupled-v tothe .said two branches? 4'. A--radio receiver forsimultaneously recei-vin a plurality of carrier waves of differentfrequenf" cies' modulated by the'A same signals, comprising` Y means forab'stracting .energy fromsaidfradiated carrier waves, means `forsegregating said diiler, y

ent lfrequencyA wavesI in separate circuits, means for converting `thereceived waves-of the different frequencies to the same frequency,Vmeanslfor` modif-ying the relativeV -phases `of .thel received waves lofY- diierent A frequencies "in such manne;1 that the Ydirectly, receivedwaves are inthelfsame phase, yafcircuit comprisingf'two branches?,means'V Y -for impressing-saidconvertedidirect waves/arid echoeslproduce'd Joy., reflections .in such-manner upon fsaidlast-mentionedfcircuit...that:inone Y l branch said! direct vvwaves are:additive` in. eifeot and said echoes lsubstantially neutralize :eachother-andin the other branch saiddirect waves substantially neutralizereach other4` and.. said echoes are nadditive in effect-and an :outputcire l cuit including van indicating device coupled to saidtwobranches.k Y f 1 5. In a radio signalling system avtransmittercomprising means for generatirigaYplural-ityof carrier- -wavesf ofdifferent lirequencies, means` for mo'dulatin-gsaidf carrierwaves-.withthe same-sig-l nals--and means for radiatingsaidmodulatedcare rier' waves; vandY raf receiving- -circuit comprisingmeans for Aalostracting` energy from said radiated i carrierY waves,means for Lsegregat-.ng saiddifferl-4 ent frequency waves in separate.circuitsf means for converting -thereceived waves of ldifferent frenquencies to the sameI frequency, .means for-anodiy"tying-tire relativephases ofthefreaeivedwavesof `diiierent frequencies in suchllfmanner.that-the' 'directly received waves are' `thesame phase,

` the input ,'fcir e f two receiving branches, transformers orfcouplingsaid separatev Acircuits to` Vsaidwtwol receiving branches, thesecondary windings of lsaid transl- `for-mers beingdividedintosections-andlav section of each secondary/winding being -connectedv in`series aiding relationfintheA input circuit lof-fone of saidreceiving-branches andlanothensection of each secondary winding :beingconnected `in series opposed relation in the otherm'i `Saidwre -ceivinglbranches i-andoutput circuits 'fior` saidA re- ,intotwqnaives@neinaltereaehiseeonaarywind;

winding being. connected tion in the other in` the yinput circuit of onelof an indifcatingdevicercqupledwtcs d. wo branches 6. Inv a fradiosignallingrfsystema .ftransm tter comprising means f waves of differ"lating'gs'aid :carrie w .W l f l 'all i 'l enemies, meana forj mqduavesWith thfsame signals ,receivrie 'arrange 'ent comprising'bstraciine'enrgygfwih radiated means or a o einewaves:numismaticasaidim.diff

ferent: frequency far/ayesf'inf Vvseparate jc` cuitsnat least one'heterdyne oscillator for cnyertg-th received'waves ofcthetwofrequenciestothe 'same frequency, a phase adjuster forjmodifying therelative'phases ofthe-received waves of thetwo frequencies in suchmanner Y i',hat"the directly receiv'edvwa'ves are in the samephase; two.receiving branhejs",.transformers.forpupimg said separate circuits tosans wei receiving. t c ches, the 'sjeep'ndarywinemgs. of; said. dans@gers beingspnp :winding beinglconnectedin series id ingrelation L, i@PQQ. g branches, and'theother yha'lfof each, s condary quimy. `lbetweenY n being a 'Whole edual "toV the intersyairof'umje'in secridsibetweritheinstais when thejdirect wave and the first echo Wave lare and( meansfor :radiating said-1 :no matedy pa er t y v Y Y radiated' carri waves,lters, for segregating said two different Certificate of Correctionn,Patent No.v 2,350,702. June 6, 1944.

EDWARD HILL ULLRICH It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows: Page 2, second column, line 45, for sin p1(t-T2) read sinw1(t- T2); and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Oice.r

Signed and sealed this 29th day of August, A. D. 1944.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.

Patent No; 2,350,702.

` Certificate of` Correction June 6, 1944. EDWARD HILL ULLRICH Y f It ishereby certified that error appears in the printed specification oftheabove numbered patent requiring correction as follows: Page 2, secondcolumn, line `45,

for sin 1(t-T2) read sin Mt-T2); and that the said Letters Patent sholdbe i read with this correction therein that the saine may conform to therecord (of the case in the Patent Office. f

Signed and sealed this 29th day of August, A. D. 1944.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.

